Function dbUpgradeTable

Updates a specific table. Used e. g. by CONTENIDO setup to create or update
tables. Function logic: 1 .) Check, if the table exists 2a.) If not, create it
with the field specification, exit 2b.) If the table exists, check, if the field
exist 3 .) If not, try to find the field using previous names (if specified in
$field like 'name1,name2') 4a.) If the field hasn't been found, create the field
as specified, exit 4b.) If the field has been found using a previous name (if
specified) rename the column to $field 5 .) As the field has been found, check,
if the field's type is matching 5a.) If the type is matching, exit 5b.) If the
field's content type is not matching, try to convert first (e.g. string to int
or int to string), then use the upgrade statement if applicable

Note about the upgrade statement: - the code must be eval'able - the code
needs to read $oldVal (old field value) and needs to set $newVal (value to which
the field will be set) - $oldVal might be empty if the field didn't exist -
$tableValues['fieldname'] contains the already existing values